gets/sets the current fill colour for the collider
fill
Examples
const A = $.makeCircleCollider($.w/2,$.h/2-50,50);
A.fill = "#54d89f";
const B = $.makeCircleCollider($.w/2,$.h/2,50);
B.fill = "rgb(252,232,223)";
const C = $.makeCircleCollider($.w/2,$.h/2+50,50);
C.fill = "rgba(238,123,120,1)";
function update() {
A.draw();
B.draw();
C.draw();
}